Darkroom lamp



1949 J. A. M. VAN LlEMP-T 2,491,881

DARKROOM LAMP Filed Aug. 23, 1946 g Y 7 l0 5 f/ 2 1 I L3 l I Eff! i L 3 +l 6 L 1 I l l 13 l l l l ,INVENTOR:

JOHANNES A. M. VAN LIEMPT,

Patented Dec. 20, 1949 can srg'y i dTENT QFFiCEl DARKROOM LAlVIP Application August 23, 1946, Serial No. 692,524 In the Netherlands February 26, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires February 26, 1964 3 Claims.

This invention relates to electric discharge lamps, and more particularly to improvements in dark-room lamps embodying a sodium-vapor discharge tube.

Heretofore, where sodium-vapor lamps were employed for the illumination of dark rooms, it has been found necessary or desirable to use photographic materials such as chlorated silver paper, a material insensitive to the yellow rays of sodium-vapor. Difficulties, however, occur during the starting period of the lamp, i. e. during the period of time necessary for the lamp to reach its normal operating temperature or that period of time necessary for sodium vapor to attain its predetermined operating pressure. During this starting period the neon gas employed in the lamp for ignition purposes emits light, and this radiation proves harmful when working with definite color-positive emulsions.

An object of my invention is to provide a new and improved starting arrangement for electric discharge lamps by means of which the lamps will start or be placed into operation practically instantaneously at their normal operating gas temperature and pressure.

Another object of my invention is to provide means for preheating the sodium vapor and gas to its normal operating temperatures and pressure before lamp operation by an auxiliary means embodied in the lamp.

A further object of my invention is to provide an arrangement for practically instantaneously heating the sodium vapor and gas to its normal operating temperature and pressure before lamp operation by an auxiliary means, embodied in the lamp, and which upon establishment of a discharge between the electrodes of the sodium vapor lamp becomes at least part of the stabilization impedance in the discharge circuit.

A still further object of my invention is to provide an automatically operated switch, embodied within and comprising part of the lamp assembly, which becomes operative when the sodium vapor and gas have reached their normal operating temperature and pressure.

According to my invention I provide a dark room lamp which embodies a sodium-vapor discharge tube which is short-circuited during the starting period by auxiliary means arranged in the vicinity of the discharge tube. The auxiliary means may include a heating element which heats the discharge tube rapidly and approximately to its operating temperature. Under these conditions the neon gas used for ignition 2 purposes emits rays which are too weak or feeble to cause damage to the photographic materials.

The heating means or element is preferably connected in series with the discharge tube so as to constitute at least part of the stabilization impedance. If the operating voltage of the tube is half of the supply voltage, which is generally the case in actual practice, the amount of energy consumed in the heating means or element during the heating of the tube is approximatel four times greater than that consumed during the normal operation of the tube, so that the tube attains its temperature quickly.

The interruption of the bridging of the discharge tube is preferably effected by means of a switch operating automatically, which operates when the discharge tube has reached a suillciently high temperature. ihis switch may be a thermal switch, for example a bimetallic switch, which is heated by the discharge tube itself.

Further features and advantages of my invention will appear from the following description of species thereof.

Fig. 1 illustrates a U-shaped sodium-vapor discharge tube with a heating means or element 2 arranged between the legs thereof. A resistance wire 3 of the heating means or element 2 is connected, at one end, to the electrode d of the tube and, at the other end, to one pole or button of terminal base 5 of the lamp. The other pole of the base 5 is connected to the electrode 6 of the tube. As shown, the electrodes 4 and E are of the cold starting, self-heating type, that is, they are not preheated before starting 0 of the discharge in the lamp.

I provide control means or switch l, which automatically controls the electrical energizetion of the tube l in accordance with the temperature of the tube i. One way in which this may be accomplished is by the provision of a thermal switch having a pair of contacts 8 and 9, one or both of which may be actuated by bimetallic elements. In the embodiment of my invention illustrated contact 8 is shown as a stationary contact, whereas contact 9 is supported and operated by a bimetallic strip it, which in the unheated condition is in engagement with contact 8. The switch i is designed to maintain its contacts closed until the temperature of the tube I attains a predetermined Value, at which time the strip It moves contact 9 out of engagement with contact 8. The electrode 5 is connected, in addition, to fixed contact 8 of the bimetallic switch. Bimetallic strip ill of the switch is connected to the electrode 6 of the tube. The discharge tube I operates as a heating element for the bimetallic strip 10, and the strip is so arrangedl that it minimizes the direct influence of the heating means or elements 2, The bimetallic switch '5 is closed in the cold state, so that in this case the heating means or ele ment 2, 8 is directl connected to the bu-tons of the lamp base. Consequently, the discharge tube is rapidly heated to a high temperature when current is supplied, the bimetallic strip being so changed. in shape that the short-circuit across the tube is removed and the discharge can take place directly in sodium vapor. During operation the heating means or element 2, t is connected in series with the discharge tube l.

The tube l is surrounded in the usual manner by a removable double walled Dewar bulb H. Bulb 55 may be formed as illustrated comprising a double envelope having an evacuated or air filled compartment therebetween. This bulb may be supported by a disc-shaped base member 52, which is grooved an ularly to receive the end of bulb ii. The above described tube switch '5, and the heating means 2, 3, may be supported by the base 52 in the manner ilustrated. Base 5 is secured to the bottom surface of base it and the two connections to the buttons of base 5 extend through member 52. A suitable means, such as a knurled thumb screw it, may be employed to hold the bulb l l in place.

Upon connection of the lamp assembly to a source of power, such as an alternating current circuit, the contacts 8 and 5 which are normally closed in the unheated or low temperature condition, short-circuit the electrodes of tube i and connect the heating means 2 directl across the source of power through the associated conductors connected to base 5. When the temperature of the tube l attains a predetermined value established by the design or adjustment of switch 3, the contacts 8 and 9 are opened by virtue of the action of the bimetallic strip !8 so that the short-circuit is removed across the electrodes of tube i. In addition, the switch '1 effects the series connection of the tube 1 and the heating means across the source. In this manner, the switch i selectively controls the heating means and the tube i, so that initially when the temperature is low the heating means alone is energized, and subsequently connects the means 3 and the tube l in series across the source of power. It will be observed that by permanently connecting one terminal of the heating means to the source and the other terminal to one electrode of the tube l the number of circuit connections is reduced to a minimum and the means 3 may serve a dual function, namely, may serve as a heating means during the starting operation and as a stabilizing impedance during running or operating conditions.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A lamp assembly comprising a gaseous electric discharge device containin a pair of electrodes and a starting gas and a vaporizable metal which emit light of different colors, an electrit cal heating element adjacent said discharge de vice and adapted, h n energized, to heat said discharge device to approximately its normal operating temperature, means to connect said heating element in series with said discharge device across a source of current supply, a starting circuit shunting said discharge device and including a normally closed thermal switch mounted in heat-receiving relationship to said charge device and adapted to open only upon heating of said discharge device to approximatelyits normal operating tem erature.

2. A. lamp assembly comprising a gaseous electric discharge lamp containing a pair of electrodes of the cold starting, self-heating type and a filling of gas and a vaporisable metal which emit light of different colors, electrical heating means adjacent said discharge lamp and adapted, when energized, to heat said lamp to its normal operating temperature, thermal switch means mounted in heat-receiving relationship to said lamp and const'ucted to be actuated only when said lamp has attained its normal operating temperature, and means connecting said switch to sh0rt-circuit said lamp during its starting e *iod to remove the shortecircuit upon actuation of the switch.

3. A assembly comprising a U--shaped gaseous electric discharge lamp containing at its ends a pair of electrodes of the cold starting, self-heating type and a filling of gas and a vaporizable metal which emit light of different colors, electrical heating means mounted between the legs of said discharge lamp and adapted, when energized, to heat said lamp to its normal operating temperature, thermal switch means mounted in heat-receiving relationship to said lamp on the outer side of its bent portion and constructed to be actuated only when said lamp has attained its normal operating temperature, and means connecting said switch to short-circuit said lamp during its starting period and to remove the short-circuit upon actuation of the switch.

JOI-IANNES ANTONIUS MARIA VAN LIEMPT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,020,736 Pirani et a1. Nov. 12, 1935 2,085,530 Inman et a1 June 29, 1937 2,087,747 Young July 20, 1937 2,286,789 Dench June 16, 1942 2,291,355 Simmon July 28, 1942 

